Directionless Reconfigurable Optical Add and Drop Mesh Node

ABSTRACT

A reconfigurable optical add/drop multiplexer (ROADM) with a multiplexer, demultiplexer, and a wavelength cross-connect unit provides directionless capabilities. The ROADM allows a signal not to be limited to a particular direction when added at an optical network node, for example. The signal can be sent to other directions of the optical network node. Furthermore, the ROADM allows the wavelengths of add and drop signals to be changed and hence is “colorless.”

BACKGROUND OF THE INVENTION

The present invention is generally related to mesh nodes in opticalnetworks and, in particular, to mesh node systems with add/dropcapabilities.

Current optical networks are mostly DWDM (Dense Wavelength DivisionMultiplexing) networks in which particular wavelengths of light definecommunication channels so that multiple communication channels can becarried on a single optical fiber. An ITU (InternationalTelecommunications Union) standard specifies the particular channelwavelengths and the spacing between these channels. DWDM is based uponWDM (Wavelength Division Multiplexing), an earlier ITU standard in whicha smaller number of wavelength channels are carried by an optical fiberwith the channels further spaced apart. It should be noted that the termDWDM, as used herein, refers to the more inclusive sense of wavelengthdefinition of communication channels so as to include the ITU WDM andDWDM standards, unless specifically stated otherwise.

Whether in an optical network or not, a mesh node is located at theintersection of at least three, typically four or more, network links.Hence the name, “mesh.” The network links provide alternate networkdirections for communication signals leaving the node. A systemoperating at a mesh node directs the communication signals entering thenode from one network direction to another direction as instructed. Forexample, the destination address of a signal wavelength instructs a nodeon the direction of these signals are to be sent.

A mesh node can also provide a location for signals to be dropped fromthe network or added to the network. The “drop” signals are typicallyintended for a client located near the node. The “add” signals aretypically originated from clients near the node for transport by thenetwork. The facility to add and drop signals is a particular problemfor optical networks due to the particular nature of light.

Current DWDM mesh node systems have add and drop functions on thebi-directional links connected to a mesh node. In particular, the addfunction is located on the link leading away from the node and the dropfunction on the link leading to the node. Thus a problem arises for theadd signals if the link is broken or the node on the other side of thelink is defective or inoperative. There is no alternate link to reroutethe add signals.

Hence there is a need for flexible mesh node systems in which add anddrop signals can be rerouted. The signals are not limited to particulardirections, and hence are considered “directionless.”

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of a mesh node in a network.

FIG. 2A illustrates the organization of a current mesh node system for aWDM network;

FIG. 2B shows the details of the patch panel in the FIG. 2A system; FIG.2C shows the details of the direction block in the FIG. 2A system.

FIG. 3A illustrates the organization of a mesh node system in accordancewith one embodiment of the present invention; FIG. 3B illustrates thedetails of the add/drop block of the FIG. 3A mesh node system; FIG. 3Cillustrates the details of the direction block of the FIG. 3A system.

FIG. 4 shows organization of the FIG. 3A mesh node system into twonetwork elements in accordance with an embodiment of the presentinvention.

It should be noted that in the drawings above, elements having likefeatures or functions in different drawings often have the samereference numerals to better aid an understanding of the presentinvention and its embodiments.

DETAILED DESCRIPTION OF THE INVENTION

In an overview of the present invention:

One aspect provides for a system for a mesh node connected to aplurality of directions in a DWDM network. The system has a patch panel,a plurality of direction blocks, and at least one add/drop block. Thepatch has a plurality of ports and optical waveguides connecting eachport to other ports of the plurality of ports. Each direction block isconnected to one of the plurality of patch panel ports and selectivelysends wavelength signals from the port to, and sends wavelength signalsto the port from one of the plurality of directions. The at least oneadd/drop block is connected to one of the plurality of patch panel portsand sends wavelength signals from at least one client to the another oneof the plurality of patch panel ports and selectively sends wavelengthsignals from the another one of the plurality of patch panel ports tothe at least one client. The wavelength signals sent from the at leastone client to the another one of the plurality of patch panel portscomprise add signals to the mesh node and the wavelength signalsselectively sent from the another one of the plurality of patch panelports to at least one client comprise drop signals from the mesh node.

For a system for a mesh node connected to a plurality of directions in aDWDM network, the system having a patch panel and a plurality ofdirection blocks connected to the patch panel for sending signals fromone of the plurality of directions through the patch panel to another ofthe plurality of directions, another aspect provides for at least oneadd/drop block. The add/drop block has a first optical amplifier havingan output terminal and an input terminal; a demultiplexer connectedbetween the output terminal of the first optical amplifier and the atleast one client; and a wavelength-selective switch connected betweenthe patch panel and the first optical amplifier whereby thewavelength-selective switch selects drop signals from the patch panel tothe at least one client.

Still another aspect provides for a system for a mesh node connected toa plurality of directions in a DWDM network. The system has a patchpanel; a plurality of first blocks connected to the patch panel onlysending signals from one of the plurality of directions through thepatch panel to another of the plurality of directions; and at least onesecond block connected to the patch panel only adding and droppingsignals at the mesh node.

FIG. 1 illustrates a mesh node graphically. In an optical mesh network,the single representative node 10 in FIG. 1 is connected by opticalfibers which carry optical signals to and from the node in a pluralityof directions to other nodes of the network. In this example, eightdirections are shown. The double-headed arrows 11-18 each represent atleast two optical fibers, one optical fiber to carry signals away fromthe mesh node 10 to the next node connected by the optical fiber andanother optical fiber to carry signals from the node connected by theoptical fiber to the mesh node. In passing, it should be noted thatoften “degrees,” rather than directions, is used to designate thecapacity of the equipment or system which implements a node in anetwork.

FIG. 2A shows the organization of a current mesh node system whichimplements a mesh node in a DWDM network. An example mesh node of fourdegrees is shown for ease of explanation. It should noted also that in aDWDM mesh node no regeneration of signals is required as the signalspass through the node from source to destination directions, in contrastto the 3R (retime, reshape and regenerate signal) operations performedat nodes in networks.

The current system has a patch panel 20 with ports 21A-D for each of thefour directions. The patch panel 20 provides paths for the opticalsignals entering the panel 20 through one port from one direction to theother ports in the other directions of the mesh node. FIG. 2B is arepresentation of the patch panel 20 which is implemented with opticalwaveguides, optical fibers specifically, and connectors. In the meshnode of FIG. 2A, the port 21A is connected to the other ports 21B-21D;the port 21B is connected to the other ports 21A, 21C-21D; the port 21Cis connected to the other ports 21A-21B and 21D; and the port 21D isconnected to the other ports 21A-21C. Of course, the multidegree patchpanel 20 can easily be modified to accommodate more directions for themesh node.

Connected to each of the patch panel ports 21A-21 D is an arrangement ofoptical devices, represented by a block 22A-22D. The details of theblocks 22A-22D are illustrated in FIG. 2C in which an example block 22is shown. Each block 22A-22D has an optical cross-connect device 30, twooptical amplifiers 33 and 34, a multiplexer 32 and a demultiplexer 35.The optical cross-connect device 30 includes a wavelength-selectiveswitch 31 which has multiple input terminals (as indicated by the broadarrow) connected through a single port 21 to the other patch panel portsof the patch panel 20. Another input terminal of the switch 31 isconnected to an output terminal of the multiplexer 32 whose inputterminals carry signals to be added at the mesh node. An output terminalof the switch 31 is connected to an input terminal of the opticalamplifier 33 which, in turn, has its output terminal connected to theoptical fiber leading away from the mesh node. As instructed by controlsignals, the wavelength-selective switch 31 selectively sends anywavelength signal combination at the switch's multiple input terminalsto the common output terminal. The unselected wavelength signals areblocked from the output terminal.

The optical fiber carrying incoming signals to the mesh node isconnected to an input terminal of the optical amplifier 34 whose outputterminal is connected to an input terminal of the patch panel port 21.The optical cross-connect element 30 divides the amplified incomingsignals and sends a fraction of the signals to the demultiplexer 35which separates out the wavelength channel signals to be dropped.

Each direction block 22A-22D has facilities to add and drop signals forlocal clients. To translate the dropped optical wavelength signals toelectrical signals for the client, the input terminals of a transponderdevice (not shown) are connected to the output terminals of thedemultiplexer 35. Likewise, the output terminals of a transponder deviceare connected to the input terminals of the multiplexer 32 to translatethe add electrical signals from the client to optical wavelength signalsfor network transport.

It should be noted that the FIG. 2A system requires that add signals betied to the direction in which added signals are to travel from the meshnode and are not “directionless.” A client places the add signalsthrough the multiplexer 32 of a particular direction block 22A-22D foroutgoing signals from the mesh node, i.e., for a particular link in thenetwork. If the link for that direction is broken or the node at theother end of the link is faulty, there is no way for the add signals tobe rerouted through the network to reach the intended destination nodewithout severely disrupting the operation of the mesh node, such asrerouting the optical fibers in the patch panel 20, also termedrecabling the patch panel.

To ameliorate this situation, the present invention provides for anadd/drop block, such as the block 33 illustrated in FIG. 3A, whichallows for the add signals at the mesh node to be rerouted around afaulty link. According to one embodiment of the present invention, theadd/drop block fits into any open port of a patch panel 30. The add/dropblock provides a way for signals to be added and dropped at the meshnode without disrupting the mesh node system installation describedpreviously. There is no need to reconfigure the patch panel 30 andconsequently the waveguides of the panel 30 need not be optical fibersto allow recabling of the panel. The waveguides can be selected on othercriteria, such as performance, costs and maintenance.

The add/drop block 33 according to one embodiment of the presentinvention has two optical amplifiers 43 and 44, a multiplexer 42 and ademultiplexer 45, as shown in FIG. 3B. Furthermore, the block 33 alsoincludes an optical cross-connect device 40 with a wavelength-selectiveswitch 41. A plurality of input terminals of the switch 41 is connectedto a port of the patch panel 30 as shown by the broad arrow; the outputterminal of the switch 41 is connected to the input terminal of theoptical amplifier 43. The output terminal of the optical amplifier 43 isconnected to the demultiplexer 45 which separates the optical signals tobe dropped. The drop signals are received by clients through the inputterminals of the transponder devices, here represented by the dotted box49. Signals to be added at the mesh node from clients are generated atthe output terminals of transponder devices, here represented by thedotted box 48, and received by the input terminals of the multiplexer 42whose output terminal is connected to the input terminal of the opticalamplifier 44. The output terminal of the optical amplifier 42 isconnected to the patch panel port.

The result is that the add and drop signals are directionless; they arenot limited to a particular direction. This is very useful. If a link tocarry an add signal (or its destination node) is broken or faulty, theadd signal is simply rerouted to a link in another direction to avoidthe link (or node). Furthermore, if the clients connected to themultiplexer 42 and demultiplexer 45 are suitably adapted, the add anddrop signals for the node become “colorless” also, i.e., the signals arenot limited to particular wavelengths. Instead, the wavelength(s) forthe add signals can be changed by the client and the wavelength(s) ofthe drop signal(s) can be selected by the wavelength-selective switch41. Rerouting can be performed by direction and by wavelength channel.

As shown by FIG. 3C, the direction blocks 32B-32C are simplifiedversions of the FIG. 2A direction blocks. The multiplexers anddemultiplexers are removed since there is no need for add and dropfunctions.

The FIG. 3A system was drawn to illustrate the advantageous differencesover the FIG. 2A system. Hence the add/drop block 33 was substituted forone of the direction block and the direction blocks 32B-32D handle thethree remaining directions. To handle the four directions, a patch panelof higher degree, e.g., a patch panel of eight degrees can be used forfour direction blocks 32, along with an add/drop block. If more add ordrop capacity is required, a second add/drop block can be connected tothe patch panel.

As stated earlier, the blocks of FIGS. 2A and 3A are representations ofan arrangement of optical devices to help explain the organization ofmesh nodes. In fact, the mesh node system illustrated by FIG. 3A can beorganized as a single or multiple network elements for networkoperations. FIG. 4 shows one organization in which a mesh node isorganized into two network elements. The optical amplifiers 43, 44 andthe multiplexer 45 and demultiplexer 42 are part of a network element51, and the patch panel 20 and the optical cross-connect devices40A-40D, are part of a second network element 52. The two networkelements 51 and 52 have separate IP addresses, or node target IDs. Theadd wavelength signals entering the cross-connect device, 40A in theFIG. 4 example, in the second network element 52 can be sent out throughthe multidegree patch panel 20 and the other cross-connect devices40B-40D in the network element 52 in any desired outbound directionselectively through software configuration.

In accordance with the present invention, the add signals are notlimited to any direction, and hence are “directionless,” and the pathsof signals through the mesh node can be reconfigured. Likewise, in theinbound direction to the mesh node, any wavelength signals entering thesecond network element 52 through a cross-connect device 40B-40D and themultidegree patch panel 30 can be selectively routed to thecross-connect device 40A facing the first network element 51 fordropping. And, as mentioned earlier, the mesh node can be “colorless,”which permits the wavelengths of the add and drop signals to be changed.The mesh node system can be scaled upwards easily by this flexibility.

Network control of the mesh node is communicated with conventionalnetwork communications pathways. For example, DCN (Data CommunicationsNetwork) extensions can be used for provisioning, or reprovisioning upona break in a network link, the mesh node. In an embodiment with networkelements 51 and 52, the switching functions of the network node proper,i.e., network element 52, are separated from add and drop functionsperformed by network element 51. All the transponder, multiplexer, anddemultiplexer devices, mounted in cards are advantageously located in asingle network element, which then communicates with a second meshnetwork element containing only cross-connect devices and a multidegreepatch panel. A network element is dedicated to send and receivewavelength signals to and from any desired direction of the mesh node.In addition, the wavelength signals and the direction in which theyleave the node are reconfigurable through software and require no manualrecabling of the patch panel.

A further advantage is the reduction in optical element count. Since anadd/drop block handles the add/drop functions for all directions of themesh node, there is no need for the add signal multiplexers and dropsignal multiplexers for the direction blocks, as shown by blocks32B-32D, and the corresponding client transponders for translatingsignals between the electrical and optical domains are eliminated foreach direction. Devices, such as transponders, multiplexers anddemultiplexers, are expensive. The costs of a mesh node system arelowered and the organization of a mesh node is simplified.

This description of the invention has been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise form described, and manymodifications and variations are possible in light of the teachingabove. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical applications.This description will enable others skilled in the art to best utilizeand practice the invention in various embodiments and with variousmodifications as are suited to a particular use. The scope of theinvention is defined by the following claims.

1. A system for a mesh node connected to a plurality of directions in aDWDM network, said system comprising: a patch panel having a pluralityof ports and optical waveguides connecting each port to other ports ofsaid plurality of ports; a plurality of direction blocks, each directionblock connected to one of said plurality of patch panel ports, eachdirection block selectively sending wavelength signals from said portto, and sending wavelength signals to said port from one of saidplurality of directions; and at least one add/drop block connected toanother one of said plurality of patch panel ports, said add/drop blocksending wavelength signals from at least one client to said another oneof said plurality of patch panel ports and selectively sendingwavelength signals from said another one of said plurality of patchpanel ports to said at least one client; whereby said wavelength signalssent from said at least one client to said another one of said pluralityof patch panel ports comprise add signals to said mesh node and saidwavelength signals selectively sent from said another one of saidplurality of patch panel ports to at least one client comprise dropsignals from said mesh node.
 2. The mesh node system of claim 1 whereinonly said add/drop block includes comprises multiplexer anddemultiplexer devices.
 3. The mesh node system of claim 2 wherein eachdirection block comprises: a first optical amplifier having a outputterminal for sending signals to one of said plurality of directions andan input terminal; a first wavelength-selective switch having aplurality of input terminals connected to said one of said plurality ofpatch panel ports and an output terminal connected to said first opticalamplifier input terminal, said first wavelength-selective switchselectively sending wavelength signals from said plurality of inputterminals to said output terminal; a second optical amplifier having aninput terminal receiving signals from said one of said plurality ofdirections and output terminal connected to said one of said pluralityof patch panel ports.
 4. The mesh node system of claim 2 wherein saidadd/drop block comprises: a third optical amplifier having an outputterminal and an input terminal; a demultiplexer connected between saidoutput terminal of said first optical amplifier and said at least oneclient; and a second wavelength-selective switch connected between saidanother one of said plurality of patch panel ports and a third opticalamplifier; whereby said wavelength-selective switch selects drop signalsfrom said another one of said plurality of patch panel ports to said atleast one client.
 5. The mesh node system of claim 4 wherein saidadd/drop block further comprises: a fourth optical amplifier having aninput terminal and an output terminal connected to said another one ofsaid plurality of patch panel ports; and a multiplexer connected betweensaid input terminal of said fourth optical amplifier and said at leastone client; whereby said add signals to said mesh node pass through saidfourth optical amplifier and said multiplexer.
 6. The mesh node systemof claim 1 further comprising: a second add/drop block connected betweenstill another one of said plurality of patch panel ports, said secondadd/drop block sending wavelength signals from at least a second clientto said still another one of said plurality of patch panel ports andselectively sending wavelength signals from said still another one ofsaid plurality of patch panel ports to said at least a second client;whereby said wavelength signals sent from said at least a second clientto said still another one of said plurality of patch panel portscomprise add signals to said mesh node and said wavelength signalsselectively sent from said still another one of said plurality of patchpanel ports to said at least a second client comprise drop signals fromsaid mesh node.
 7. The mesh node system of claim 1 wherein said opticalwaveguides of said patch panel are incapable of changing patch panelport connections.
 8. For a system for a mesh node connected to aplurality of directions in a DWDM network, said system having a patchpanel and a plurality of direction blocks connected to said patch panelfor sending signals from one of said plurality of directions throughsaid patch panel to another of said plurality of directions, at leastone add/drop block, said an add/drop block comprising: a first opticalamplifier having an output terminal and an input terminal; ademultiplexer connected between said output terminal of said firstoptical amplifier and said at least one client; and awavelength-selective switch connected between said patch panel and saidfirst optical amplifier; whereby said wavelength-selective switchselects drop signals from said patch panel to said at least one client.9. The add/drop block of claim 8 wherein said add/drop block furthercomprises: a second optical amplifier having an input terminal and anoutput terminal connected to said patch panel; and a multiplexerconnected between said input terminal of said second optical amplifierand said at least one client; whereby add signals to said mesh node passthrough said second optical amplifier and said multiplexer.
 10. A systemfor a mesh node connected to a plurality of directions in a DWDMnetwork, said system comprising: a patch panel; a plurality of firstblocks connected to said patch panel only sending signals from one ofsaid plurality of directions through said patch panel to another of saidplurality of directions; and at least one second block connected to saidpatch panel only adding and dropping signals at said mesh node.
 11. Themesh node system of claim 10 wherein said at least one second block isprovisioned by setting a wavelength-selective switch in said at leastone second block to select signals from said patch panel to drop at saidmesh node.
 12. The mesh node system of claim 10 wherein said pluralityof first blocks are provisioned by setting a wavelength-selective switchin each first block to select signals from said port to send to one ofsaid plurality of directions.
 13. The mesh node system of claim 10wherein said patch panel comprises non reconfigurable opticalwaveguides.
 14. The mesh node system of claim 10 wherein only said atleast one second block comprises multiplexer and demultiplexer devices.